1). Field of the Invention
This invention relates to an electrosurgical instrument of the kind used for electrosurgical arthroscopy.
2). Discussion of Related Art
Arthroscopic surgery is often used to treat degenerating cartilage. Cartilage on the back of the patella, for example, tends to wear down due to overuse into collagen fibrils having bases attached to remaining viable cartilage. The fibrils themselves then tend to cause acceleration in the degeneration process of the viable cartilage, and the xe2x80x9cwearxe2x80x9d debris from the fibrils irritates the joint lining. This irritation can be a source of pain as the fibrils break down and break off as debris which may necessitate joint replacement.
There are several interventions a surgeon may choose when addressing these lesions of the articular cartilage. While some surgeons feel the lavaging (irrigating) the joint is sufficient, many more surgeons endeavor to remove the excess material in an attempt to decrease the xe2x80x9cwearxe2x80x9d debris that originates from these strands of cartilage. One common way of addressing these lesions is with the use of mechanical shavers as are commonly used in arthroscopic surgery to xe2x80x9cshavexe2x80x9d off the long fronds of cartilage. This procedure is called a chondroplasty.
In another arthroscopic treatment method, a surgeon inserts an electrosurgical probe through an incision or opening formed in a body of a patient. Radio frequency (RF) power is then provided to an electrode at the end of the probe, which creates ohmic heating of an area surrounding the electrode. The fibrils are denatured by the heat when the electrode is brought into contact with the fibrils, which causes the fibrils to congeal together, forming an intact surface.
In order to effectively denature the fibrils, it is required that the fibrils be exposed to a relatively high temperature, for example, 70xc2x0 C. or greater. Such high temperature not only denatures the fibrils, but has the potential to cause permanent damage to the viable cartilage to which the fibrils are attached. The high temperature causes chondrocyte death because the cartilage does not regenerate. The typical high temperature profiles of non-thermally controlled prior art probes may also deliver too much thermal energy which may also cause avascular necrosis (AVN) of the underlying bone structure, requiring total joint replacement.
Thus, what is needed is a surgical probe which can effectively address the fibrils while protecting viable cartilage. The probe should be able to deliver a controlled amount of energy for thermal treatment with a variable temperature profile to treat the different tissues at the surgical site.
According to one aspect of the invention, an electrosurgical instrument is provided, having a holding formation, an elongated probe, at least one electrode, and a conductor. The elongated probe is connected to and extends from the holding formation. The at least one electrode is located on an end of the elongated probe opposing the holding formation, and forms at least part of an electrode structure that has a leading edge and a face. The at least one electrode is locatable so that the face is substantially in a horizontal plane and the leading edge is above the horizontal plane. The conductor extends along the elongated probe and has a portion connected to the at least one electrode to provide RF power thereto. The at least one electrode creates a temperature profile with a temperature adjacent to the leading edge being higher than a temperature adjacent to the face.
The leading edge and the face are preferably on a single electrode.
The leading edge may have a smaller radius of curvature than the face. The face may be substantially flat. The leading edge may be substantially sharp. The leading edge may point in a direction away from the horizontal plane.
There is preferably no material of the electrode directly below the leading edge in the horizontal plane.
The electrode may have a convex cam surface between the leading edge and the face. The convex cam surface may extend up to the leading edge.
The at least one electrode may have a trailing edge on a side of the face opposing the leading edge. The trailing edge may be at substantially the same distance from the horizontal plane as the leading edge.
The electrode may have an electrode opening therein. The electrode opening may have a diameter which is less than 50% of a diameter of the electrode measured in the same plane. The electrode opening may extend through the face. The electrosurgical instrument may further include a thermally conductive plug in the opening at or near the face, and a thermocouple in contact with the thermally conductive plug. The thermally conductive plug, at or near the face, is preferably made of an electrically insulating material.
Preferably, a line at right angles to the horizontal plane is at an angle with respect to an axis of the elongated probe. The angle may, for example, be at least 30xc2x0.
A lower surface of the elongated probe may be above the horizontal plane.
The holding formation may, for example, be a handle.
A method is provided for treating degenerative collagen fibrils, having bases attached to viable cartilage. A surface of an electrode structure is located adjacent to viable cartilage. A temperature profile is generated having a low temperature adjacent to the face and a high temperature at a location further from the viable cartilage than the face. The electrode structure is moved in a direction substantially parallel to a plane of the viable cartilage. Such movement first exposes each fibril to the location of the temperature profile having the high temperature, whereafter the surface moves over the fibrils.
Preferably, the location on the temperature profile having the higher temperature passes through an imaginary plane normal to the plane of the viable cartilage before the face passes through the imaginary plane.